Speedy drug monitoring with new molecule

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A new way to quantify the amount of a drug in a patient's bloodstream, within seconds and with nothing more high-tech than a domestic digital camera and some computer software, has been developed by scientists in Switzerland.

There are many drugs that require careful monitoring and dose adjustment to optimise therapy and prevent harmful side effects. These include blood-thinning agents like warfarin, anti-rejection drugs used for organ transplants, and some antibiotics.

But making these measurements is time consuming, costly, and inconvenient for patients and doctors, because samples have to be sent away to a laboratory.

Now, the Institute of Chemical Sciences and Engineering, Lausanne, Switzerland, scientist Rudolf Griss, writing in Nature Chemical Biology, has developed an ingenious chemical technique to make light of the problem - so that a sample as small as a single droplet of blood can be tested and emit light of a certain colour and intensity that corresponds to how much drug is present.

To do this, Griss and his colleagues used a molecule, called luciferase, that can produce light. Coupled to this is a molecule that acts like a coloured filter, meaning that the light that is given off is a red colour. But if the drug of interest is present, it pushes out this red filter, switching the light to a blue colour.

A photograph taken with a low-cost digital camera and fed into a simple computer programme was then analysed to measure the relative amounts of red and blue light given off, which could then be used to calculate the concentration of the drug in the blood sample. The team demonstrated that the technique could accurately measure the levels of drugs including the medically important immune-suppressants cyclosporin, tacrolimus and methotrexate, as well as the heart drug digoxin and a common anti-epilepsy agent called topiramate.

Making chemical detectors for each of the molecules was not difficult.

In the future it seems likely that a simple kit can be developed for home use. This would comprise of a piece of paper impregnated with the test chemicals onto which a drop of blood is squeezed, photographed with a smartphone and then analysed with an app. One possible shortfall, however, is that patients are rarely ever on just one drug - many are taking multiple agents at once. These other agents could all interfere with the test, so careful road-testing of the technique will be needed before it can be introduced commercially.